Process of preparing pure alumina



Patented Dec. 16,1930

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' TOKYO, JAPAN rnocnss or PREPARING PURE ALUMINA 11o Drawing.Application filed July 6, 1927, Serial No. 203,869, and in JapanFebruary 3, 1927.

- This invention relates to a process of pre paring pure aluminaconsisting in treating mipure alumina containing silicon, iron,ferro-silicon, or oxides of iron as impurities,

pare pure aluminafrom impure alumina with chlorine or hydrochloric acidgas while heated to a temperature above 200 (3., with or without thesimultaneous use of reducing agents, The object of the invention is toprecontalnlng any-or all of the above substances as impurities in a verysimple and economica ccording to this invention, when the impure aluminacontains silicon, iron, and

ferro-silicon, and no oxides of iron, it heated with chlorine gas orhydrochloric acid gas to a temperature above 200 C.

When it contains oxides of iron besides other im urities,suitablereducing agents such as car on monoxide may be mixed with theabove named gases; or a suitable quantity of carbon may be added to thealumina itself. When impure alumina containing the above namedimpurities is treated with chlorine or hydrochloric acid gas at anelevated temperature above 200 0., with or without the addition ofreducing agents-according to the presence or absence of oxides ofiron,the silicon, iron, and ferro-silicon, are all chan ed into volatilesilicon tetrachloride and ferrlc chloride respectively, while oxides ofiron if an are reduced to iron which is at once change into ferric,chloride- As both silicon tetrachloride and ferric chloride arevolatile they are at once removed from the alumina leaving it quitepure.

Ewample l.-A clay of following composition was taken as raw material:

Percent Ignition -loss. 15. 01 Silica 19.15 Ferric oxide 16.12'

Alumina- 50. 90

:This clay is mixed with 20 r its weight of carbon, and-the mixture isheated in an electric furnace, according to'the known process, andalumina thus produced is se arated from the ferro-silicon which is formeby the "duction. Such alumina is not pure and A still contains 2.6% ofsilicon and 3.52% of iron a part of which being as'iron oxide. Thisimpure alumina is heated in an atmosphere of chlorine gas containing 10%ofcarbon monoxide gas to 450 C. for two hours. The. remainin product ispractically. pure alumina in WliCh iron and silicon are redu ed to moretraces.

AND TORAO KURITA, OF TOKYO Example 11 Taking 200 grms. of clay,

the same as in Example I, 25 grms. charcoal product 'is practically apure alumina containing only traces of iron and silicon.

The alumina which is obtained by reducing 'cla or bauxite in electricfurnace acoord- I ing to own or any other convenient process usuallycontams a considerable quantity of s1l1con, iron, and ferro-silicon, andsometimes oxides of iron as impurities. As these im-' I purities areuniformly fused together with alumina, the separation of, suchimpurities from it'to obtain pure aluminahas hitherto been diflicult. 1

According to this invention, those'impurities are changed into volatilecompounds and thereby easily removed from the crude alumina, so thatpractically pure alumina having only' traces of said impurities can bevery easily obtained. The crude alumina "prepared in an electric'furnaceis very hard and consequently is ground topowder with difliculty. Whenpieces of such impure alumina are treated with chlorine or hydrochloricacidgas at an elevated temperature, these gases penetrate through themass and volatilize off the said-impurities from it. The penetration isso effective that crude alumina may be subjected to the treatment evenin lump form. After the treatment with chlorine or hydrochloric. acidgas, the lumps of alumina become so loose and brittle, owing to theremoval of iron and silicon; that it can I be easily ground to powder. I

Crude alumina such as prepared by so called wet process, containinoxides of iron but no silicon can also be simi arly treated accordingtothis invention and pure alumina free from iron can be obtained.

We claim:

1.. The process of purifying impure alumina containing silicon, iron;ferro-silicon and oxides of iron as impurities which comprises heatingthe impure alumina with a carbonaceous reducing agent to reduce themajor portion of any llOIl oxide contained therein and thereaftersubjecting the alumina to the action of chlorine gas and carbon monoxideat an elevated temperature until the iron and silicon constituents havebeen removed as their volatile chlorides.

2. The process of purifying impure alumina containing silicon, iron,ferro-silicon and oxides of iron as impurities which comprises heatinthe impure alumina with a carbonaceous re ucmg agent to reduce any 11011oxlde contalned therein and thereafter subjecting the alumina to theaction of chlo-' rine gas at an elevated temperature until the iron andsilicon constituents have been removed as their volatile chlorides. v

In testimony whereof we aflix our signatin-es.

' 'TSUNEO SUZUKI.

' HIROSHI TANAKA.

TORAO KURITA.

